The invention relates generally to video capture circuits and methods, and more particularly to digital video and/or audio capture circuits and methods that captures data embedded in vertical blanking intervals, such as close-caption data, ancillary data or other data.
Graphics adapters, sometimes referred to as graphics controllers, are known which enhance the performance of display systems such as laptop computers, desktop computers, portable computing units and other devices. Graphics controller chips are increasingly employed to accommodate digital video from DVD sources, cable television, and other video sources wherein the video is displayed along with graphics information on a computer screen. In a multimedia system this may allow users to both watch movies, and perform other computer functions simultaneously.
Video signals such as NTSC format signals utilize vertical blanking regions (e.g. vertical blanking intervals) to contain non-active video data such as closed-caption data and other data as known in the art. Graphics controller chips are known that have video capture circuits to suitably capture video data received through an analog or digital video decoder. Video decoders are known that generate ancillary data blocks (ANC) which may include for example audio data or other data. The ancillary data is typically included in the vertical blanking interval. Once the video and ancillary information is obtained, a host processor typically analyzes the vertical blanking interval data and ancillary data to determine what the data is and then subsequently presents the data properly on a display device.
Video decoders are known that partially decode vertical blanking interval data and insert the encoded vertical blanking information into the horizontal blank regions in the form of ancillary data so that the host processor need not do as much decoding and processing, thereby improving the performance of the system. This may become particularly important where multi-tasking is required by the host processor.
Also known are single port video chips, separate single port audio chips and single port VBI chips. A problem can arise with separate single port digital video and audio capture circuits since such circuits have to accommodate separate types of data such as video data, audio data, and other digital data, such as ancillary data embedded as part of a vertical blanking interval. Each type of data typically needs to be captured and routed to a proper processing engine or display unit in an efficient manner, otherwise the loss of data can occur. For example, where the video data may be a live feed, any loss of information will result in an unacceptable display quality due to missing data.
Also, if systems use separate decoders for audio data and/or ancillary data, it may be possible to pass the decoded audio directly to a speaker to guarantee that the information is not lost. However, such information may not necessarily be in synchronization with received video. Although such a system may not require writing of audio information to a frame buffer or other storage device, it may risk nonsynchronization of audio and video during display. Hence, storage of some data may be present.
Multiport capture circuits can sometimes afford improved performance by allowing different ports to receive and process different types of data. However, such multiport capture circuit can require additional circuitry that adds cost and size to an integrated circuit.
Consequently, there exists a need for a single port digital video and/or audio capture circuit that accommodates the processing of vertical blanking interval data, such as closed-caption data, audio data, or any other suitable data. It would desirable if such a single port capture circuit and method would be employed in a graphics chip that could interface with a host processing unit to help reduce the loading on the host processor.